The following Patent Document 1 discloses a fuel cell system to drive a load using a fuel cell and a battery, the fuel cell system including two converters for the fuel cell and the battery. This fuel cell system makes the converter for fuel cell and the converter for battery operate in a coordinated manner so as to supply electric power to the load stably. The system is provided with a relay as a connector on an electric power supply path to connect the battery and the load. The system is configured to turn off the relay when the system stops and to turn on the relay to connect the battery with the load when the system starts and a voltage supplied to the load from the fuel cell exceeds a battery voltage. This configuration prevents wasteful consumption of battery power during the system stop as well as rush current from flowing to the load side from the battery side at the time of relay connection.